Lose Control Of Captured Thralls After Joining A Clan

Game mode: Private Main Branch Server
Problem: Bug
Platform: PC

A new player had progressed to Lv20 by themselves. They had captured and placed a number of thralls in their base, fighters.
Then they were invited and joined our clan. Once they had accepted, all the thralls which they had owned before joining the clan were no longer controlled by him or anyone else in our clan.
They couldn’t be moved, killed or interacted with. We had to get an admin to kill them.

This has happened again to another player. They start off, setup a base with some thralls guarding it. Then join someones clan, now the thralls can’t be controlled, moved or killed.